Age-related macular degeneration (ARMD) constitutes a severe threat to vision, and the frequency of cases of ARMD is tending to increase because of lengthening lifetimes and various environmental factors and daily exposure to light, which factors are also combined with genetic predispositions.
ARMD results in a progressive loss of macular vision cells. It is the major cause of poor vision in industrialized countries for people aged more than fifty, but it affects the macula only. It therefore cannot lead to complete blindness.
There are two main forms of ARMD:
Dry or atrophic ARMD which is characterized by the formation of small spots or “drusen” under the retina and by atrophy of the retinal pigmentary epithelium. There exists no treatment for this type of ARMD, in particular by means of a laser.
Wet or exudative ARMD is characterized by the presence of abnormal blood vessels or neovascularization. These vessels are fragile, can bleed, leak, develop, and progressively destroy the macula. As a general rule, in order to be able to see them, it is necessary to perform angiography which displays them accurately. Angiography using fluorescein reveals fluid leaks and retinal neovascularization, while angiography using indocyanine green reveals choroidal and occult new vessels. Angiography consists in injecting dye into the veins in order to observe retinal and choroidal blood vessels better and in order to photograph the retina after various lengths of time have elapsed.
The first signs of the disease can be seen only by an ophthalmologist, and they are detected by examining the back of the eye, and possibly also by performing angiography with fluorescein or indocyanine green. The patient perceives symptoms only once the disease has already reached an advanced stage. There is no pain.
The most common symptom is a loss of visual acuity: initially in the form of a need for increased light levels when reading. Fewer details can be seen and certain features of the face disappear or certain letters or words in a phrase disappear when reading. Another symptom is alarming and makes people consult quickly: this is the appearance of straight lines that become deformed.
At a more advanced stage, central vision is highly degraded (a black spot in the center of the field of vision): faces are no longer recognized, and reading and writing become impossible. Peripheral vision is conserved and allows the patient to be mobile and remain independent.
Various treatments are made available to patients suffering from ARMD. Therapeutic indications cannot be described in greater detail insofar as numerous treatments are presently under evaluation. In addition, none of those treatments enables ARMD to be cured. It is possible only to halt degeneration or to slow down the advance of the disease.
There are thermal-type treatments in which a heating effect is looked-for and used, and there are other treatments.
The two thermal-type treatments are photocoagulation by laser treatment and thermal therapy through the pupil.
Photocoagulation by Laser Treatment
This is the first treatment to have demonstrated effectiveness on a clinical form of new vessels; visible neovascularization outside or beside the fovea.
This treatment is difficult to perform. The purpose of the treatment is to burn the new vessels by releasing a high temperature in the vicinity thereof. More precisely, the coherent laser beam interacts with the back portion of the retina (the pigmentary epithelium) which absorbs light. This reaction raises the temperature at the back of the epithelium, thereby also leading in harmful manner to definitive lesions in the photodetectors.
Transpupillary Thermal Therapy (TTT)
Transpupillary thermal therapy is treatment that consists in using a laser to heat the zone for treatment as in laser photocoagulation treatment. However, in this treatment, the laser beam is used to raise temperature to a smaller extent than with conventional photocoagulation treatment. This is in an attempt to avoid the above-mentioned lesions due to using a laser that gives off high temperatures. Nevertheless, in order to obtain a therapeutic effect while heating less strongly, it is necessary to apply the laser beam for a longer duration (several tens of seconds). This is described in international patent application WO 02/45633. In particular, the recommended duration of irradiation for this treatment lies in the range 30 seconds (s) to 40 s. Unfortunately, any laser treatment is precision treatment that requires the zone for treatment to remain stationary throughout the duration of the treatment. Keeping a patient's eye stationary for several tens of seconds is not possible, unless the treatment is applied under anesthesia.
There are also two non-thermal type treatments constituted by conventional medication and dynamic phototherapy.
Medication Treatments
At present, no treatment by medication has been successful. The treatments that have been studied the most are those relying on supplying additional oligo-elements and vitamins: vitamins A and E, selenium, zinc, . . . . The idea is to cause the retina to operate under better metabolic conditions and thus limit the risk of accumulating the waste associated with aging.
Dynamic Phototherapy (OPT)
Dynamic phototherapy is a recent method which consists in combining a photosensitive drug with a “non-thermal” laser (one that does not burn the retina), in contrast to the lasers used for photocoagulation.
The photosensitive drug, such as that sold under the trademark Visudyne®, for example, is injected intravenously into the body of the patient. This drug rapidly reaches the abnormal blood vessels of the retina where it becomes fixed to the inside walls of these new vessels. Thereafter, the portion of the macula that is to be treated is illuminated with a red laser, e.g. at a wavelength of 689 nanometers (nm), and for a duration of 90 s. The laser beam serves to activate the photosensitive drug which leads to a sequence of chemical reactions taking place inside the new vessels, causing the abnormal vessels in the retina to become occluded, and subsequently to disappear. More particularly, the action of the laser beam on the molecules of the photosensitive substance serves mainly to generate singlet oxygen (1O2), which is the main agent serving to occlude abnormal retinal vessels.
The latest studies have given results that are very satisfactory, with 60% of patients treated presenting visual acuity that is stabilized or improved. Nevertheless, that method presents several drawbacks. The first drawback is associated with patients being photosensitized, which obliges them to avoid any exposure to the sun for a relatively long period of time, generally of the order of 48 hours (h). Another drawback is associated with injecting a drug (a photosensitive substance) that is expensive, thus making the treatment expensive, it being understood that the treatment needs to be repeated in order to be effective. Finally, with some patients, injecting a photosensitive drug can lead to side effects that are harmful.